332 EVENINGS AT THE MICROSCOPE. 



granular ; but there is a very manifest tendency to a 

 fibrous character in its texture, the fibres being directed 

 from the exterior towards the interior, supposing the 

 lobes to have their points in contact. 



Let us now look at the margin of the disk. Here are 

 attached twenty-four slender tentacles, six in each qua- 

 drant formed by the divergent ribs, or radiating canals. 

 Each tentacle springs from a thickened bulb, which is 

 imbedded in the margin of the disk ; it is evidently 

 tubular, but the tube is not wider in the bulb than in the 

 filament. The general surface is rough, with projecting 

 points, which in some assume a very regular spinous 

 -appearance, and the tentacle terminates in a blunt point. 

 The discal part of the bulb is fringed with a row of minute 

 bead-like spherules. Around the edge of the circumference 

 •of the disk, on the exterior, are arranged eight beautiful 

 and conspicuous vesicles, or organs for hearing. They are 

 placed in pairs, those of each pair being approximate, and 

 appropriated to each of the quadrants of the circle. Each 

 of these organs consists of a transparent globe, not enve- 

 loped in the substance of the disk, but so free as to appear 

 barely in contact with it: it contains a single otolithe, 

 of high refractive power, placed, not in the centre, but 

 towards the outer side. The inexperienced naturalist, on 

 first seeing these organs, would unhesitatingly pronounce 

 them eyes, and the otolithe, or ear-stone,* the crystalline 

 lens. They are, however, pretty certainly, rudimentary 

 organs of hearing; the crystalline globule or otolithe 

 being capable of vibration within its vesicle. Their 

 •exact counterparts are found in many of the smaller 

 Medusae, as we lately saw in the Thcmmantias. 



The disk is endowed with an energetic power oc con- 

 traction, hy which the margin is diminished, exa 3tly like 

 that of a Medusa swimming; and the tentacles have also 

 the power of individual motion, though in general this is 



* See note on page 56. 



